A sintered metal bearing is used under a state in which a lubricating oil is impregnated into inner pores thereof. The lubricating oil impregnated into the sintered metal bearing seeps into a sliding portion with respect to a shaft, which is inserted along an inner periphery of the sintered metal bearing, along with relative rotation of the shaft, to thereby form an oil film. The sintered metal bearing is configured to rotationally support the shaft through this oil film. Such a sintered metal bearing has excellent rotational accuracy and quietness, and hence has been suitably used as a bearing device for a motor to be mounted to various electrical apparatus such as information apparatus. Specifically, the sintered metal bearing has been suitably used in a spindle motor for an HDD or a disk drive for a CD, a DVD, and a Blu-ray disc, a polygon scanner motor for a laser beam printer (LBP), or a fan motor.
As an example of sintered metal bearings of this type, there has been known a sintered metal bearing in which, in order to achieve further improvement in quietness and prolongation of life, dynamic pressure generating grooves serving as a dynamic pressure generating portion are arrayed in a predetermined pattern on an inner peripheral surface and/or an end surface of the bearing. As a method of molding the dynamic pressure generating grooves in this case, there has been proposed what is called dynamic pressure generating groove sizing. In this sizing, for example, a sintered compact is press-fitted to an inner periphery of a die, and is compressed in an axial direction by upper and lower punches so that a molding die on an outer periphery of a sizing pin that is inserted in advance along an inner periphery of the sintered compact is caused to bite into the sintered compact. With this, a pattern of the molding die, specifically, a pattern corresponding to the dynamic pressure generating grooves is transferred onto an inner peripheral surface of the sintered compact. In this way, the dynamic pressure generating grooves are molded into a predetermined pattern (refer, for example, to Patent Literature 1).
As an example of the array pattern of the above-mentioned dynamic pressure generating grooves, array regions of a plurality of the dynamic pressure generating grooves may be formed at two positions on the inner peripheral surface of the bearing separately from each other in the axial direction. In those array regions of the dynamic pressure generating grooves, the dynamic pressure generating grooves are arrayed in an orientation of causing a lubricating oil to be drawn to an axial center in each of the array regions of the dynamic pressure generating grooves. In view of this, there has been proposed a fluid-dynamic bearing in which, in order to prevent generation of a negative pressure between the array regions, a recessed portion (large diameter portion on the bearing side or small diameter portion on the shaft side) is formed in the inner peripheral surface or an opposed outer peripheral surface of a shaft as a lubricating oil reservoir (refer, for example, to Patent Literature 2).